The government was yesterday ordered to release the minutes of cabinet meetings where the invasion of Iraq and its legality was discussed in a move which exposes the decision to go to war to fresh scrutiny.

Richard Thomas, the information commissioner, ordered disclosure because of the "gravity and controversial nature" of the subject. There was, he said, "a widespread view that the justification for the decision on military action in Iraq is either not fully understood or that the public were not given the full or genuine reasons for that decision."

It is the first time the commissioner, who adjudicates on Freedom of Information Act disputes, has ordered the release of cabinet minutes, traditionally regarded as meriting special protection.

The Cabinet Office, which said it was considering the decision, has 28 days to appeal to the information tribunal.

Thomas said the case for disclosure was strengthened by controversy over the attorney general's advice on the legality of military action and ministerial resignations at that time.

Tony Blair has been accused, notably by Clare Short, then international development secretary, of stifling cabinet debate before the invasion on March 20 2003, with Gordon Brown's acquiescence. Leaked documents indicate Blair assured US president George Bush two months earlier that he would go along with the invasion but did not tell the cabinet.